The present invention relates to a lighting unit for a reading unit which is provided in an image reading apparatus such as a scanner or the like which reads an image on a document, or in an image forming apparatus such as a copier, a digital copier, a facsimile or the like, the image reading apparatus, and the image forming apparatus.
More specifically, the present invention relates to a lighting unit which illuminates an area (image reading area) where an image is read on a document placed on an image reading apparatus or on an image forming apparatus, the image reading apparatus provided with this lighting unit and a reading unit such that reflected light from the image reading area is imaged on an imaging sensor and image information is obtained by the imaging sensor, this image forming apparatus being provided with a similar reading unit to the above.
In an image reading apparatus such as a scanner or the like which reads an image on a document, or in an image forming apparatus such as a copier, a digital copier, a facsimile or the like, a lighting unit to illuminate an area where an image (image reading area) is read on the document placed on the image reading apparatus or the image forming apparatus is provided.
In these apparatuses, it is necessary to evenly illuminate the image reading area to accurately read the details of the image on the document.
There have been proposed many techniques to evenly illuminate the image reading area (for example, see Japanese patent publication numbers 2004-157213, 2005-027082, 2002-142082, 2005-241681, 2006-042016, and 2006-067551)
All apparatuses disclosed in Japanese patent publication numbers 2004-157213, 2005-027082, 2002-142082, 2005-241681, 2006-042016, and 2006-067551 have a lighting unit, and a light source, and a mirror which reflects illumination light from such a light source is provided with the lighting unit.
In the lighting unit disclosed in Japanese patent publication number 2005-027082, an LED (light-emitting diode) as a direct light source which illuminates a document directly, and an LED for reflected lighting are separately provided, which creates a high cost.
In addition, as the lighting unit disclosed in Japanese patent publication number 2005-027082, in a structure where a plurality of cylindrical-type LEDs from which a directional characteristic of emitted light is narrower than that from a surface-emitting-type LED and which is relatively large-sized and simply arranged side by side, an arrangement pitch of the LEDs is wide, and thereby unevenness of light in the image reading area can easily to occur.
The lighting unit disclosed in Japanese patent publication number 2002-142082 has 2 reflecting surfaces which are in a concave shape and face an LED.
In Japanese patent publication numbers 2005-241681, 2006-042016, and 2006-067551, a method of preventing unnecessary light scattering and lighting a document effectively is disclosed.
In Japanese patent publication numbers 2005-241681 and 2006-042016, a method of reducing the unevenness of light according to a structure of an LED arrangement is disclosed.
In these lighting units, the image reading area on a document is evenly lit by use of a mirror arrangement.
In apparatuses disclosed in Japanese patent publication numbers 2004-157213, 2005-027082, 2002-142082, 2005-241681, 2006-042016, and 2006-067551, the light amount of direct light from a light source and the light amount of indirect light by a mirror are asymmetric in a light source side and a mirror side of the image reading area on the document by light attenuation due to reflection by a mirror, or by a difference of each of the light path lengths.
By the way, for example, in a case where a document in which a piece which is cut away from another document (hereinafter, a second document) is pasted on an original document (hereinafter, a first document), what is called, a cut-and-paste document, is read, when light is emitted from outside of a pasted second document toward the pasted second document and when the light is emitted from the pasted second document toward the outside of the pasted second document, the state of a shadowing occurrence around the pasted second document may change.
Therefore, in the apparatuses disclosed in Japanese patent publication numbers 2004-157213, 2005-027082, 2002-142082, 2005-241681, 2006-042016, and 2006-067551 where the amount of emitted light is asymmetric in the light source side and the mirror side of the image reading area on the document, there is a possibility that either shadowing in the light source side or shadowing in the mirror side may occur as a result.